A wide variety of paving practices and specialized equipment has been developed over the years in an attempt to optimize paving quality. Paving contractors are often tasked with meeting certain project specifications relating to paving quality. If specifications are met or exceeded, the paving contractor may receive bonus payments. If specifications are not met, at minimum bonus payments may be forfeited, and in some instances expensive and lengthy rework of a construction site may be required. Moreover, in recent years there has been a trend toward increasing contractor responsibility for long-term pavement durability. One factor increasingly recognized as important to the durability of a paved surface over many years is smoothness. Careful pre-paving preparation of the surface to be paved can level the grade and reduce irregularities in the surface profile. Level grades and relatively regular surface profiles tend to result in enhanced smoothness of a mat of paving material placed upon the surface. Nevertheless, there are limitations to the extent to which contractors can practicably prepare a surface prior to paving. Different contractors are also often responsible for preparation of the surface to be paved versus actual paving of the surface, tending to disperse responsibility among unrelated parties. Limitations in the controllability of machines used in paving systems can also affect the achievable smoothness for a given paving project.
As alluded to above, in many instances the surface to be paved may have an irregular profile, even after preparation via one or more passes with a cold planer, reclaimer, recycler, or other machine. Numerous examples of machine hardware and controls are known in the art which attempt to compensate for irregularities in the profile of a surface to be paved. In one conventional technique, the relative height of a screed of a paving machine may be varied to control the amount of paving material deposited by the paving machine as it passes over a surface. Bumps, dips and other irregularities can be under-filled, over-filled, etc., to lessen the extent to which a mat of paving material reflects the irregularities in the surface. An instrument known as an averaging ski is often coupled with a paving machine, and provides data to the paving machine which indicates the presence of changes in a profile of the surface to be paved. The paving machine operator or control system can adjust screed height in response to data from the averaging ski to achieve a smoother mat than might otherwise be possible. Sonic sensors, stringlines and other mechanisms for providing data used in controlling and monitoring the screed and other aspects of a paving system are also well known and used with increasing frequency in the paving arts.
In addition to varying the processes, controls and hardware used in paving to optimize smoothness and other aspects of paving quality, engineers have developed a variety of means for measuring the smoothness of a surface once it has been paved. Smoothness measurements may be used to verify whether project specifications have been met, and to validate paving strategies intended to provide smooth results. One common practice is to use a relatively complex and expensive piece of equipment known as an inertial profiler or a simpler California Profilograph. The apparatus is typically pushed or towed and includes one or more sensors to sense changes in the profile of a surface. Either type of smoothness measurement may be used during paving to measure smoothness as paving progresses, by the paving contractor, third parties contracted to measure smoothness values or by Department of Transportation personnel to assess whether a particular paving project has met or exceeded smoothness specifications. While profilographs have been shown to be effective, they have certain shortcomings, notably expense, and can be unwieldy when used during paving or to transport. U.S. Pat. No. 5,549,412 to Malone is one example of a paving system using a profiling device in conjunction with the paving machine. In Malone, a profiler is used to collect data on a base surface. An asphalt paver is provided with a similar profiler that measures smoothness of a fresh mat of asphalt laid by the paver. In Malone, profiler and paver position are determined via GPS, and smoothness of the mat may be plotted based on data inputs from the profilers. Malone's system may be suited to its intended purpose, but is relatively complex, expensive and unwieldy.